1. Field of the Invention
The invention relates to a coil device having a drum core disposed on a board, the drum core having a coil formed thereon and the board having a lead terminal.
2. Related Art
FIG. 3 is a sectional view of a conventional coil device 1. In FIG. 3, reference numeral 2 denotes a ring core made of a magnetic material such as ferrite; 3, a drum core having collars 3a, 3c and a winding part 3b and being made of a magnetic material such as ferrite; 4, a coil formed on the winding part 3b; 5, an insulating board having a lead terminal 6; and 7, an adhesive for fixing the drum core 3 to the board 5. Here, an end part 4a of the coil 4 is connected to a front end part 6a of the lead terminal 6 that is bent midway.
While the lead terminal 6 is usually fixed to the board 5 by insert molding, once a strong force has been applied to the lead terminal 6 in a direction indicated by an arrow A, the end part 6a thereof is moved in a direction indicated by an arrow B. As a result, a tensile force is produced at the end part 4a of the coil 4, thereby breaking the coil 4.
A conventional coil of this type is also constructed as shown in, e.g., FIGS. 4 and 5. That is, in FIGS. 4 and 5, a coil device 101 includes: a board 102 made of an insulating material; a drum core 103 being fixed to the top surface of the board 102 and made of a magnetic material such as ferrite; a coil 104 formed on a winding part 103c between upper and lower collars 203a, 203b of the drum core 103; a pot core 105 enclosing the drum core 103 and having an open space at a lower end; and a plurality of lead terminals 106 (three in the case shown in FIGS. 4 and 5) inserted into the board 102 so as to project toward one side (leftward in the case of FIGS. 4 and 5) from the bottom of the board 102 while passing through the board 102.
The winding lead terminal of the coil 104 is led out sideways from the pot core 105 through the open space 105a provided at the lower end of the pot core 105 so as to be bound up around an end part 106a projecting sideways from the lead terminal 106.
However, in the thus constructed coil device 101, the end part 106a of each lead terminal 106 projecting sideways must have a certain length so that the winding lead terminal of the coil can be bound up around the end part 106a. Therefore, the end part 106a projects sideways by a relatively large length from the board 102 and the pot core 105. When this coil device 101 is to be mounted on a mounting board for forming circuits of various devices, the substantial mounting area is increased since the end part 106a of each lead terminal 106 projects by a large length. This makes the mounting board large in structure, thus running counter to the needs for downsizing the mounting board.